1. Field of the Invention
The invention relates to movable barriers such as overhead doors and the like, particularly openers of the type in which a drive force is applied to the overhead door by a motor assembly.
2. Description of Related Art
One of the problems which must be addressed in designing and engineering overhead door openers for garage doors and other large, heavy doors is the provision of automatic, safe, and reliable stopping of the door at open and closed positions. Most garage door operators include a head unit containing a motor and a transmission, which may comprise a chain drive or a screw drive coupled to a garage door for opening and closing the garage door. As discussed in co-pending U.S. patent application No. 467,039, which is incorporated herein by reference, such garage door openers also have included optical detection systems located near the bottom of the travel of the door to prevent the door from closing on objects or on persons that may be in the path of the door.
Such garage door operators typically include a wall control which is connected via one or more wires to an operator or head unit to send signals to the head unit from a remote location to cause the head unit to open and close the garage door, and to light a work-light. Such prior art garage door operators also include a receiver for receiving radio frequency transmissions from a hand-held code transmitter or from a keypad transmitter which may be affixed to the outside of the garage or other structure. These garage door operators typically include adjustable limit switches which cause the garage door to reverse direction or which halt the motor when the travel of the door causes the limit switch to change state, either in the open position or in the closed position. In the prior art, internal limit switches have been provided within the head unit, and external limit switches have been provided at various locations outside of the head unit. It may be appreciated that the limits of travel typically must be custom set during or after installation of the unit within the garage. In the past, such units have had mechanically adjustable limit switches which are typically set by an installer. The installer may need to inspect the door, the wall switch and the head unit in order to make adjustments in order to set the limit switches properly. This, of course, is time consuming and results in the installer being required to spend more time than is desirable to install the garage door operator.
Requirements from Underwriters' Laboratories, the Consumer Product Safety Commission, and/or other organizations require that garage door operators sold in the United States must, when in a closing mode and contacting an obstruction having a height of more than one inch, reverse and open the door. Prior art garage door operators also include systems whereby the force which the electric motor applied to the garage door through the transmission might be adjusted. Typically, this force is adjusted by a licensed repair technician or installer who obtains access to the inside of the head unit and adjusts a pair of potentiometers, one of which sets the maximum force to be applied during the closing portion of door operation, the other of which establishes the maximum force to be applied during the opening of door operation.
Such a garage door operator is exemplified by an operator taught in U.S. Pat. No. 4,638,443 to Schindler. However, such door operators are relatively inconvenient to install and invite misuse because the homeowner, using such a garage door operator, if the garage door operator begins to bind or jam in the tracks, may obtain access to the head unit and increase the force limit. Increasing the maximum force may allow the door to move past a binding point, but also may undesirably apply increased force at the bottom of its travel.
Electrical limit switches are operated by physical contact between actuators and stops. However, the mechanical features of the switches and their electrical contacts are subject to strain, degradation caused by exposure to the surrounding environment, and other factors. As a result, the limit switch set points may drift from their proper settings, and, under automatic operation, the overhead door may not close or open as desired. One particular problem can arise when a homeowner, using a remote control unit, transmits a "close" command while driving away from a garage, but the garage door erroneously reverses automatically as it reaches the closed position. In this situation, the garage door may be left open for an extended time, unknown to the homeowner, permitting access to the garage and possibly an attached residence as well. In order to readjust limit switch set points in prior art systems having internal limit switches, a user may be required to inspect the actuators from the vantage point of a ladder and, after determining the direction and amount of adjustment required, physically change their positions.
Commonly assigned U.S. patent application No. 467,039 discloses an improved control arrangement for garage door operators and the like which addresses several of the above problems. However, there is a continuing need for further improvement, particularly with respect to facilitating installation of a commercially practical apparatus addressing these problems.